Die casting machine including sequentially acting compound pistion assembly machine

ABSTRACT

THE PISTON ASSEMBLY OF A DIE CASTING OR PLASTIC INJECTION MACHINE INCLUDES INNER AND OUTER CONCENTRIC PISTONS. THE INNER PISTON IS DIRECTLY DRIVE WHILE THE OUTER PISTON IS DRIVEN THROUGH THE MEDIUM OF A STACK OF CONICAL WASHERS SO THAT WHEN THE METAL OR PLASTIC BEING CAST ATTAINS A PREDETERMINED PRESSURE, THE WASHERS COLLAPSE AND ARREST MOTION OF THE OUTER PISTON WHILE THE INNER PISTON CONTINUES TO MOVE, GREATLY INCREASING THE INTERNAL PRESURE AT FINAL CHILLING.

p 1971 R. K. WHITEHEAD. sR.. ETAL 3,505,871

DIE CASTING MACHINE INCLUDING SEQUENTIALLY ACTING COMPOUND PISTON ASSEMBLY Filed May 1, 1969 INVENTORS HARRY C. WHITEHEAD BY M 7/? ATTORNEYS RICHARD K. WHITEHEAD, SR. mcumu K. WHITEHEAD,JR.

United States Patent "ice DIE CASTING MACHINE INCLUDING SEQUEN- TIALLY ACTING COMPOUND PISTON ASSEM- BLY MACHINE Richard K. Whitehead, Sr., 1631 Northgate Wood Road NE. 30329; Richard K. Whitehead, Jr., 2044 Breckenridge Drive NE. 30324; and Harry C. Whitehead, 2585 Circle Wood Road NE. 30329, all of Atlanta,

Filed May 1, 1969, Ser. No. 820,869 Int. Cl. B22d 17/10, 27/12 US. Cl. 164-319 6 Claims ABSTRACT OF THE DISCLOSURE The piston assembly of a die casting or plastic injection machine includes inner and outer concentric pistons. The inner piston is directly driven while the outer piston is driven through the medium of a stack of conical washers so that when the metal or plastic being cast attains a predetermined pressure, the washers collapse and arrest motion of the outer piston while the inner piston continues to move, greatly increasing the internal pressure at final chilling.

BACKGROUND OF THE INVENTION Recent developments in the die casing art have indicated the efiicacy of injecting at a somewhat lower rate than has been conventional, and of utilizing lower injection pressures. A double-action plunger is used to build up an initial pressure near the end of the injection cycle, whereafter a secondary action builds up a higher pressure as the injection cycle is completed. This is accomplished by imparting a first stroke to the compound or doubleacting plunger after which only one part of the compound plunger is moved further to build up the higher pressure. This requires a rather complex drive system since mechanism is required to sense the attainment of the first pressure to terminate the first drive and to then switch over and effect the secondary drive.

BRIEF SUMMARY OF THE INVENTION The present invention contemplates a sequentially acting compound plunger or piston assembly wherein only a single driving entity is required and which imparts the full stroke for the piston assembly. Collapsible mechanism imparts a parallel drive to one of the piston members so that upon attainment of the first pressure, the collapsible mechanism operates to allow completion of the stroke while the forward motion of said one piston member ceases.

BRIEF DESCRIPTION OF THE DRAWING FIGURE The drawing is a longitudinal section taken through a die casting mechanism according to the present invention showing a portion of the shot cylinder as it leads to the die.

DETAILED DESCRIPTION OF THE INVENTION Reference character 10 indicates in general a conventional shot cylinder provided with the usual loading well 12 and having an end portion 14 which leads to the associated die. The plunger or piston assembly indicated generally by the reference character 16 is reciprocable within the shot cylinder 10 to inject the molten material into the die as will be understood by those skilled in the art. It has been conventional practice in the past to inject under relatively high pressures with a single piston or plunger detent and to utilize, in conjunction therewith, a relatively small gate leading to the die cavity and to impart the injecting plunger with a high rate of speed 3,605,871 Patented Sept. 20, 1971 as, for example, to complete the injecting cycle within about of a second while attaining a pressure of injection in the order of 5,000 to 12,000 p.s.i. Recent developments in die casting have indicated that if the injection cycle is slowed down and lower injection pressures used, in conjunction with a much larger gate, the castings are much denser than heretofore and can be of such quality as to be heat treatable and weldable, having reference particularly to aluminum die cast products. The result is, of course, stronger and more accurate die cast products.

In this recent development, a compound plunger or piston assembly is utilized which, in actuality, is a plunger within a plunger. The two plungers are carried together during the initial portion of the injection cycle through a predetermined stroke at which the metal in the die attainsor is subjected to an initial pressure which is relatively low as compared to ordinary injecting pressures. At this point, the compound plunger is stopped and drive is immediately imparted to one of the plunger mechanisms through a short stroke to impart the terminal pressure to the metal in the die, this terminal pressure still being low as compared with conventional die casting techniques and which may be in the order of 10,000 to 20,000 psi.

In order to achieve the sequential injecting pressure effect noted above, the present invention utilizes an inner piston 18 provided at one end with a coupling member 20 by means of which it may be attached to a single hydraulic ram mechanism which is responsible for imparting the entire injecting force both for this inner piston 18 and for the outer piston assembly indicated generally by the reference character 22. Thus, the inner piston 18 is directly connected to the ram whereas a parallel drive is imparted to the outer piston assembly 22, same being effected by the stack of conical, collapsible spring elements indicated generally by the reference character 24. The spring elements are of the form substantially as is shown and are interposed between the shoulder 26 of the coupling member 20 and the rear face 28 of the outer piston 22, a suitable cover or protective sleeve 30 being disposed in surrounding relationship to the spring washers, the cover being freely slidable with respect to the outer piston 22. The iner piston 18 projects axially through the outer piston 22 and is provided with a radially projecting annular shoulder 32 contained within the recess 34 in the rear end of the outer piston 22 a suitable plug 36 being removable received with respect to the outer piston 22 and having a suitable O ring or similar seal 38 to sealingly close the recess 34, a similar seal 40 being provided as shown to effect this action. The shoulder 32 is provided with through openings such as those indicated by the reference character 42 and the recess is filled with a quantity of oil as indicated by the reference character 44 so that, as will hereinafter be described, a dash pot or damping action is efiected upon the attainment of relative motion between the inner and outer pistons as will appear.

The outer piston may be provided with a berrylliumcopper tip 46 threadedly engaged with the inner end of a main body portion 48 of the outer piston, as is conventional practice in the art. This tip provides a recess 50 substantially is is shown and the inner piston 18 is provided with an exial bore 49 provided with a divider strip 51 for circulating coolant into and out of the recess 50, and the coupling member 20 having a coolant inlet 52 and a coolant outlet 54 on opposite sides of the divider strip 51.

The ram which controls the stroke of the coupling member 20 and thus the total stroke of the inner pistion 18 simply drives the same until the predetermined final or terminal pressure is achieved in the metal within the die whereas the collapsible means 24 is so constructed and arranged as to collapse at the lower or initial pressure desired. For example, the collapsible means 24 may be adapted to collapse at about 6,000 p.s.i. and allow approx imately inch travel of the inner piston 18 at this pressure beyond the outer piston. Whereafter the collaspsible means 24 will bottom. Since the collapsible means is responsible to the initial pressure to collapse and allow lost motion between the outer piston relative to the inner pistion advances so as to maintain the same pressure (i.e. 6,000 p.s.i.) in the molten metal were it not for the provision of the damping or dash pot mechanism 32, 34. The purpose of the dash pot mechanism is to slow the retreating tendency of the outer piston and allow a higher terminal pressure to build up the die dast metal so that, in eiiect, the collapsible means 24 is resisting retreating of the outer piston with a predetermined :force supplemented by the additional force effected by the dash pot assembly which allows the total pressure of the molten metal in the die to be built up to a higher pressure than that at which the collapsible means 24 operates to allow the lost motion as aforesaid.

While discussion herein has referred mainly to die casting, it will be appreciated by those skilled in the art that the same arrangement may be applied to a plastic injection machine to accomplish densification of the final plastic products in just the same way.

'We claim:

1. In a die casting machine, in combination, a shot cylinder for receiving molten metal to be injected into a die, a piston assembly reciprocable wihtin said shot cylinder and comprising innner and outer coaxially arranged pistons, coupling means at the outer end of one of said pistons adapted for connection with a driving means for reciprocating said piston, said coupling means being rigidly connected to said piston, and collapsible drive means interposed between said coupling means and the other piston, said collapsible means being responsive to attainment of a first molten metal pressure to allow relative motion between said pair of pistons.

2. A die casting machine as in claim 1 further characterized by means for imparting driving force from said one piston to said other piston in proportion to the speed of relative movement therebetween whereby the continued motion of said one piston is effective to produce a terminal pressure within the molten metal which is greater than the first pressure.

3. A die casting machine as in claim 2 wherein said last mentioned means comprises a dash pot.

4. A die casting machine as in claim 1 wherein said collapsible means comprises a stack of conical spring washers.

5. A die casting machine as in claim 1 further including means for circulating a coolant through the inner end of the outer piston.

6. A die casting machine as in claim 5 wherein said coolant is supplied to and removed from said outer piston through said inner piston.

References Cited UNITED STATES PATENTS 2,505,540 4/1950 Goldhard 16 1-312X 3,270,383 9/1966 Hall et a1. 164-120 FOREIGN PATENTS 1,109,567 9/ 1955 France 18-30QC Ad. 66,980 5/1957 France 18-30QC R. SPENCER ANNEAR, Primary Examiner u. s. or. X.R. 18-3OQC 

